Process of casting a reactive metal



United States Patent 3,380,508 PROCESS OF CASTING A REA'CTIVE METAL Anthony Saia and Ralph E. Edeiman, Philadelphia, Pa., assignors to the United States of America as represented by the Secretary of the Army N0 Drawing. Filed Sept. 29, 1965, Ser. No. 491,463 2 Claims. (Cl. 164-42) ABSTRACT OF THE DISCLOSURE A foundry mold material for use in the casting of reactive metals and alloys thereof which consists essentially of a carbonaceous foundry material and minor amounts of a clay type foundry sand binder and water.

The invention described herein may be manufactured and used by or for governmental purposes without the payment to us of any royalty thereon.

This invention relates to a foundry mold material composition and a method for using such material for the casting of reactive metals and their alloys.

The foundry practice for casting reactive metals, such as magnesium and magnesium alloys has been to use greenor dry-sand molds while making suitable provisions within the mold for the reactiveness of the molten metal with the moisture in the sand. When molten magnesium reacts with moisture in the sand, oxide inclusions may be entrapped in the casting, and hydrogen-gas defects or pinholes may develop. The sand mold could be dried by baking at a high enough temperature to evaporate all moisture. The chemical success of this method was marred by the practical disadvantage that dried sand molds are extremely friable. Thus, resultant castings suffered from numerous sand marks and lack of definition. In order to avoid these defects, and to use green, or undried sand, agents known as inhibitors are added to the sand. These inhibitors restrain the chemical reaction of oxidation between the molten metal and the moisture in the sand. The inhibitors commonly used are sulfur, boric acid, ammonium silicofluoride, ammonium acid fluoride, ammonium borofiuoride, potassium borofluoride and various combinations of these materials. The amount and type of inhibitor used varies with the type of sand, casting section size and the pouring temperature. The lower the permeability of the sand, the higher the water content, the heavier the casting section, and the higher the pouring temperature, the more inhibitor is needed. That is, the amount of inhibitor varies inversely with sand permeability and directly with moisture content of sand, weight of casting section, and pouring temperature of metal. The inhibitors used are volatile and must be continuously replaced. This adds considerably to the operating cost of a reactive metal alloy foundry. Furthermore, there are certain magnesium alloys, such as those of the magnesium-lithium family, which cannot be successfully cast into sand molds regardless of the type or quantity of inhibitor used.

It is, therefore, an object of the present invention to provide a foundry mold material for use with a casting of reactive metals and their alloys, which mold material does not require the use of inhibitors to obtain a casting free of defects.

Another object of the present invention is to provide a foundry mold material of the above type which can be reused, provided enough binder is added to insure good forming.

A further object of the present invention is to provide a foundry material of the above type which can be sucice cessfully used for casting of alloys selected from the magnesium-lithium family.

Still another object of the present invention is to provide a foundry material of the above type which itself is inexpensive and, further, can be prepared into molds by using standard foundry equipment, thereby considerably reducing the operating costs of a reactive metal foundry.

Further objects of the present invention will in part be obvious and will in part appear hereinafter.

The foundry mold material of the present invention is comprised of a carbonaceous foundry material, such as graphite powder, a clay type foundry sand binder and water. A typical composition can be prepared by thoroughly mixing a major proportion of graphite with about 3.0 to 5.0 weight percent of western bentonite and about 2.0 to 3.0 weight percent of water. However, any carbonaceous foundry material having a 20 to 60 mesh size may be blended with a standard foundry sand clay type binder, such as southern or western bentonite, and water. After blending has been achieved, the material may be formed into a shaped mold, as for example by ramming of the material, and then permitted to cure. After use of the mold material it may be subsequently reused simply by re-mulling it.

Magnesium alloys, including magnesium-lithium alloys, were cast in molds of material of the present invention. The resultant castings were free of oxide inclusions or pinholes, and displayed a high degree of definition, as well as clean and bright surfaces. The mold material showed virtually no signs of having become friable even when magnesium-lithium alloys were cast. These favorable results are indicative that there was no chemical reaction between the molten magnesium alloys and the moisture in our inventive mold material.

The mold material of the present invention can be readily used for other metals, for example, aluminum, cast iron, and steel. Furthermore, it will be readily apparent to those skilled in this particular art that various modifications and alterations can be made without departing from the scope and spirit of this invention, and the foregoing discussion should not be construed to unduly limit this invention.

We claim:

1. A process for casting a reactive metal in a mold wherein the resultant casting is substantially free of both casting defects and any metal-mold reaction, said reactive metal being selected from the group consisting of magnesium, alloys of magnesium, and alloys of magnesium and lithium, said process comprising the steps of pouring said reactive metal, while molten, into said mold,

permitting said molten metal to solidify in said mold,

and

removing said solidified metal from said mold, said mold having been fabricated from a mixture devoid of inhibitors and consisting essentially of about 92 to 95 weight percent graphite, about 3 to 5 weight percent bentonite, and about 2 to 3 weight percent water.

2. The process as described in claim 1 wherein said graphite is from about 20 to 60 mesh size. 

